In the manufacturing processes for valve springs, from steel refining to the secondary working of wire, the techniques which are effective against non-metallic inclusions are especially important for improving fatigue properties. Attention is given to avoiding Al interaction with the molten product, and the size and shape of inclusions are controlled with a Ca-Si type synthetic slag. Decreasing the oxygen in the molten state will cause the formation of Al2 O3 undeformable inclusions and should be avoided.
To prevent both surface flaws and decarburization, conditioning of billets, control of heating temperatures in the furnace, and control of cooling temperatures after hot rolling are carried out.
Wire surfaces are shaved by using a reverse die system, and further inspection using eddy currents is used for the entire length of the wire.
By modifying SAE 9254 to achieve higher tensile strength, four new grades have been developed with increased carbon, vanadium, and molybdenum being the key elements.